Subject: A Spanish Dancer (Hexabranchus sanguineus) is showing her best moves on a Mauritian reef. This big nudibranch is not the only gastropod with swimming capacities. Some Seahares (genus Aplysia) will easily outperform the Spanish Dancer in swimming speed and endurance. Most nudibranchs with swimming abilities use this skill to avoid predation rather than as a regular form of locomotion.
Technique: Filming a frantic moving nudibranch in the water column was more difficult than I thought. Key is to keep the distance between the camera’s lens and the subject as constant as possible. You can easily center your subject in post production by using keyframes.